Krugman's excellent column on Greece
and Mankiw considers this column "thoughtful and thought-provoking".
Mankiw responses to this, challenging the idea of centralized fiscal authority (by comparing Greece and Germany to California and Washington). He askes " Does a common currency area need a centralized fiscal authority?"
Then Krugman reacts to Greg's question!
One of his previous summary of the debt crisis and the euro can clarifies a bit about his view.